Synthesis And Ion Doping On Its High-temperature Electrical Properties Of Lithium Manganese Oxide Spinel

In comparision to other positive materials, such as LiCoO2, LiNiO2, LiMn₂O₄ has the potential to be one of the widely used positive materials owing to good security, simple synthesis process, abundant resources, low price, et al.Various uses of chemical power require good performance in elevated temperature. However, commercial application of LiMn₂O₄ has been severely limited due to fast decaying of capacity in high temperature (55℃). Therefore, the paper firstly studied the synthesis process of LiMn₂O₄ and secondly doped the metal ions to improve the high temperature performance of LiMn₂O₄ with the hope of offering some reference for LiMn₂O₄'s future research.The following factors had been investigated systematically in this thesis, such as the precursor Mn(OH)2, Li/Mn ratio, holding time, and sintering procedure. At the same time, the impacts of reaction pH value on the density of precipition particles and the electrical properties of LiMn₂O₄ had been studied. And the impact of the intensity of stirring on the performance of LiMn₂O₄ had been researched. Based on the series of experiments, the best elements for LiMn₂O₄'s synthesis were concluded as following: the pH value 10.0-10.5, the intensity of stirring 300r/m around, two-stage sintering temperature ( the first-stage temperature 630℃, and the second-stage temperature 830℃-900℃), the holding time 1440min-2880min and Li/Mn ratio 1.05-1.07.This paper, firstly, researched the electrical properties of LiMn₂O₄ in room temperature (25℃) by doping TiO2. The following conclusions had been arrived at. When the doping amount of Ti⁴⁺ is 0.00, the battery capacity decayed about 17.4% after 50 cycles and with 1C rate. When Ti⁴⁺ is 0.15, the battery capacity decayed about 10.31% under the same testing conditions. The experiment used Al³⁺ to improve the electrical properties of LiMn₂O₄ by co-precipitation method. The result showed that co-precipitation was not suitable due to the dissolution of Al(OH)3 in the alkaescence solution.This paper had also researched the cycling properties of LiMn₂O₄ in high temperature (55℃) by doping Al³⁺ and Ti⁴⁺. The following conclusions had been reached. The capacity decaying of pure LiMn₂O₄ was 48.56% after 50 cycles, in 55℃and between 2.75V-4.2V. When the doping amount of Ti⁴⁺ was 0.08, the battery capacity decayed about 22.92%under the same conditions. And the electrical performance of LiMn₂O₄ had been upgraded significantly. When Al³⁺ was 0.05, the battery capacity decayed about 17.05%. In a word, the cycling performance of LiMn₂O₄ in high temperature had been improved significantly by doping Al³⁺ and Ti⁴⁺.